A conjugated diene rubber (e.g., styrene/butadiene copolymer) obtained by an emulsion polymerization method is known as a rubber for automotive tires. Under recent circumstances in which improvements in the fuel-saving performance of motor vehicles are expected, various conjugated diene rubbers which render excellent fuel-saving performance possible have been proposed.
A conjugated diolefin (co)polymer rubber characterized by (1) being a (co)polymer of a conjugated diolefin or of a conjugated diolefin and an aromatic vinyl compound, (2) having a primary amino group and an alkoxysilyl group which are bound to the (co)polymer chain, and (3) having a structure in which a monomer having a functionality of 2 or higher has been copolymerized with the (co)polymer chain and/or at least part of the (co)polymer chain has been coupled with a coupling agent having a functionality of 2 or higher has been proposed as an example (patent document 1).
As another example, a modified diene polymer rubber obtained through step 1 in which either a conjugated diene or a conjugated diene and an aromatic vinyl monomer are polymerized in a hydrocarbon solvent in the presence of an alkali metal catalyst to obtain a living polymer having an alkali-metal end and step 2 in which the living polymer is reacted with a compound represented by a specific formula to obtain the modified polymer rubber (patent document 2) is proposed.
Furthermore, a method in which a primary modification reaction for reacting a hydrocarbyloxysilane compound with the active site of a polymer having an organometal active site in the molecule is conducted and a secondary modification reaction for thereafter further reacting with the hydrocarbyloxysilane compound via a condensation reaction between hydrocarbyloxysilyl groups is conducted has been proposed as a method for producing a modified polymer which can be made to have an enhanced interaction with silica and carbon black to improve fracture characteristics, wear resistance, and low-heat-buildup characteristics (patent document 3).